The term, the diminutive form of "war" in Spanish, is usually translated as "little war", and the word, guerrilla (Spanish pronunciation: [ɡeˈriʎa]), has been used to describe the concept since the 18th century, and perhaps earlier. In correct Spanish usage, a person who is a member of a guerrilla is a guerrillero ([ɡeriˈʎeɾo]) if male, or a guerrillera if female. This term became popular during the Peninsular War, when the Spanish people rose against the Napoleonic troops and fought against a highly superior army using the guerrilla strategy.

The term "guerrilla" was used in English as early as 1809, to describe the fighters (e.g., "The town was taken by the guerrillas"), and also (as in Spanish) to denote a group or band of such fighters. However, in most languages guerrilla still denotes the specific style of warfare. The use of the diminutive evokes the differences in number, scale, and scope between the guerrilla army and the formal, professional army of the state.

The strategy and tactics of guerrilla warfare tend to focus around the use of a small, mobile force competing against a larger, more unwieldy one.[1] The guerrilla focuses on organizing in small units, depending on the support of the local population, as well as taking advantage of terrain more accommodating of small units.

Tactically, the guerrilla army would avoid any confrontation with large units of enemy troops, but seek and eliminate small groups of soldiers to minimize losses and exhaust the opposing force. Not limiting their targets to personnel, enemy resources are also preferred targets. All of that is to weaken the enemy's strength, to cause the enemy eventually to be unable to prosecute the war any longer, and to force the enemy to withdraw.

It is often misunderstood that guerrilla warfare must involve disguising as civilians to cause enemy troops to fail in telling friend from foe. However, this is not a primary feature of a guerrilla war. This type of war can be practiced anywhere there are places for combatants to cover themselves and where such advantage cannot be made use of by a larger and more conventional force.

Mao Zedong summarized basic guerrilla tactics at the beginning of the Chinese "Second Revolutionary Civil War" as: "The enemy advances, we retreat; the enemy camps, we harass; the enemy tires, we attack; the enemy retreats, we pursue."[3]:p. 124 At least one author credits the ancient Chinese work The Art of War (dating from at least 200 BC) with providing instruction in such tactics to Mao.[2]:pp. 6–7

While the tactics of modern guerrilla warfare originate in the 20th century, irregular warfare, using elements later characteristic of modern guerrilla warfare, has existed throughout the battles of many ancient civilizations but in a smaller scale. This recent growth was inspired in part by theoretical works on guerrilla warfare, starting with the Manual de Guerra de Guerrillas by Matías Ramón Mella written in the 19th century and, more recently, Mao Zedong's On Guerrilla Warfare, Che Guevara's Guerrilla Warfare and Lenin's text of the same name, all written after the successful revolutions carried by them in China, Cuba and Russia respectively. Those texts characterized the tactic of guerrilla warfare as, according to Che Guevara's text, being "used by the side which is supported by a majority but which possesses a much smaller number of arms for use in defense against oppression".[4]

Guerrilla tactics were presumably employed by prehistoric tribal warriors against enemy tribes. Evidence of conventional warfare, on the other hand, did not emerge until 3100 BC in Egypt and Mesopotamia. Since the Enlightenment, ideologies such as nationalism, liberalism, socialism, and religious fundamentalism have played an important role in shaping insurgencies and guerrilla warfare. [5]

A notable example of guerrilla warfare was during 17th century in India when the Marathas under the leadership of Shivaji attacked the surrounding kingdoms of Bijapur Sultanate and Qutub Shahi Empire, which had a numerical advantage and huge armies, but little knowledge of the geographical layout of the Western Ghats and the Deccan Plateau. He assembled small armies and constantly raided the military camps and won numerous battles even with insignificant numbers.[6]

A counter-insurgency or counterinsurgency[7] (COIN) operation involves actions taken by the recognized government of a nation to contain or quell an insurgency taken up against it.[8] In the main, the insurgents seek to destroy or erase the political authority of the defending authorities in a population they seek to control, and the counter-insurgent forces seek to protect that authority and reduce or eliminate the supplanting authority of the insurgents. Counter-insurgency operations are common during war, occupation and armed rebellions. Counter-insurgency may be armed suppression of a rebellion, coupled with tactics such as divide and rule designed to fracture the links between the insurgency and the population in which the insurgents move. Because it may be difficult or impossible to distinguish between an insurgent, a supporter of an insurgency who is a non-combatant, and entirely uninvolved members of the population, counter-insurgency operations have often rested on a confused, relativistic, or otherwise situational distinction between insurgents and non-combatants.

The widely distributed and influential work of Sir Robert Thompson, counter-insurgency expert of the Malayan Emergency, offers several such guidelines. Thompson's underlying assumption is that of a country minimally committed to the rule of law and better governance.[9]

Some governments, however, give such considerations short shrift, and their counter-insurgency operations have involved mass murder, genocide, terror, torture and execution.

Historian Timothy Snyder has written, "In the guise of anti-partisan actions, the Germans killed perhaps three quarters of a million people, about 350,000 in Belarus alone, and lower but comparable numbers in Poland and Yugoslavia. The Germans killed more than a hundred thousand Poles when suppressing the Warsaw Uprising of 1944."[10]

In the Vietnam War, the Americans "defoliated countless trees in areas where the communist North Vietnamese troops hid supply lines and conducted guerrilla warfare",[11] (see Operation Ranch Hand). In the Soviet war in Afghanistan, the Soviets countered the U.S.–backed Mujahideen with a 'Scorched Earth' policy, driving over one third of the Afghan population into exile (over 5 million people), and carrying out widespread destruction of villages, granaries, crops, herds and irrigation systems, including the deadly and widespread mining of fields and pastures.[12][13]

Some writers on counter-insurgency warfare emphasize the more turbulent nature of today's guerrilla warfare environment, where the clear political goals, parties and structures of such places as Vietnam, Malaysia, and El Salvador are not as prevalent. These writers point to numerous guerrilla conflicts that center around religious, ethnic or even criminal enterprise themes, and that do not lend themselves to the classic "national liberation" template.

The wide availability of the Internet has also caused changes in the tempo and mode of guerrilla operations in such areas as coordination of strikes, leveraging of financing, recruitment, and media manipulation. While the classic guidelines still apply, today's anti-guerrilla forces need to accept a more disruptive, disorderly and ambiguous mode of operation. According to David Kilcullen:

"Insurgents may not be seeking to overthrow the state, may have no coherent strategy or may pursue a faith-based approach difficult to counter with traditional methods. There may be numerous competing insurgencies in one theater, meaning that the counterinsurgent must control the overall environment rather than defeat a specific enemy. The actions of individuals and the propaganda effect of a subjective "single narrative" may far outweigh practical progress, rendering counterinsurgency even more non-linear and unpredictable than before. The counterinsurgent, not the insurgent, may initiate the conflict and represent the forces of revolutionary change. The economic relationship between insurgent and population may be diametrically opposed to classical theory. And insurgent tactics, based on exploiting the propaganda effects of urban bombing, may invalidate some classical tactics and render others, like patrolling, counterproductive under some circumstances. Thus, field evidence suggests, classical theory is necessary but not sufficient for success against contemporary insurgencies."[14]

Why does the guerrilla fighter fight? We must come to the inevitable conclusion that the guerrilla fighter is a social reformer, that he takes up arms responding to the angry protest of the people against their oppressors, and that he fights in order to change the social system that keeps all his unarmed brothers in ignominy and misery.

^An insurgency is a rebellion against a constituted authority (for example an authority recognized as such by the United Nations) when those taking part in the rebellion are not recognized as belligerents (Oxford English Dictionary second edition 1989 "insurgent B. n. One who rises in revolt against constituted authority; a rebel who is not recognized as a belligerent.")